Heat-sensitive recording sheet

ABSTRACT

A heat-sensitive recording sheet having a coating layer comprising a uniform dispersion of particles of a member selected from the group consisting of the iron salts of an aliphatic acid and a member selected from the group consisting of 8hydroxyquinoline and halogen derivatives thereof, as the colorforming reaction materials and an inhibitor of unusual colordevelopment selected from the group consisting of ethylenediamine tetraacetic acid and alkali metal salts thereof.

United States Patent [19 1 Takanis hiet al.

1 Jan.7, 1975 HEAT-SENSITIVE RECORDING SHEET [75] Inventors: Takashi Takanishi, Neyagawa;

Hiroshi Nishiuchi, Kadoma, both of Japan [73] Assignee: General Company, Ltd.,Osaka-shi,

Osaka-fu, Japan [22] Filed: Dec. 3, 1973 211 App]. No.1 421,142

Related U.S. Application Data [63] Continuation of Ser. No. 191,773, Oct. 22, 1971,

abandoned.

[30] Foreign Application Priority Data Nov. 20, 1970 Japan 45.102005 [52] U.S. Cl. 1l7/36.8, 117/369 [51] Int. Cl B4lm 5/18 [58] Field of Search 117/362, 36.8, 36.9

[56] References Cited UNITED STATES PATENTS 2,663,657 12/1953 Miller et a1. 117/368 12/1959 Owen 117/368 3,149,993 9/1964 Baumann et a1..... 117/369 3,414,423 12/1968 Fierke et a1 117/368 X 3,442,682 5/1969 Fukawa 117/368 Primary Examiner-Thomas J. Herbert, Jr. Attorney, Agent, or Firm-Fitzpatrick, Cclla, Harper & Scinto [5 7] ABSTRACT 10 Claims, No Drawings 1 HEAT-SENSITIVE RECORDING SHEET BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a novel heat-sensitive recording sheet. More particularly, this invention relates to a heat-sensitive recording sheet having a support with a heatsensitive layer coated on the support. These novel heat-sensitive recording sheets can be used for reproducing originals such as books, printing matters, and drawings by a thermal reproduction system, for recording diagrams in an automatic recording device by a heat pen system, and for recording, by a thermal print head, in the recording portions of computers, calculating machines, billing machines and the like.

2. Description of the prior Art Heretofore, in the prior art, various heat-sensitive sheets for reproduction systems have been known but these prior art heat-sensitive recording sheets have exhibited various disadvantages. For example, when color-forming components participating in a .colorforming reaction are formed into a single coating agent, some of these agents have been found to be only slightly soluble in the solvents commonly used. A further problem sometimes occurs when finely divided metal particles become mixed with the coating agents. Since the color-forming reaction is a solid-liquid reaction ora liquid-liquid reaction, the single coating agent itself can easily color-form as a result of metal powder contamination and slight solvent solubility with the result that the contrast of the resulting image with respect to the background is'so low that conventional recording paper cannot practically be used. Furthermore, the color-forming reaction often disadvantageously proceeds in the coating agent during storage and quality control of the resulting products is almost impossible. Still further, the product itself may deteriorate due to moisture present during storage and thereby become very unstable. Attempts to overcome these disadvantages by preparing the components of a two component system separately and forming two coating layershave been tried but this method still has the following drawbacks. The heat-sensitivityis usually so 'low'that the heat-recording member cannot follow the response of the heat-sensitive recording for the short time beating (0.01 0.01 second) periods used in a high speed reproduction device. Also, the two layer coating is not economical from a manufacturing point of view and quality control is difficult since the product is unstable. Further, the resulting print is not clear and even if a two layer structure is employed, unusual color formation at the interface thereof cannot be inhibited.

A object of the present invention is to provide a stable heat-sensitive recording sheetfree of the abovementioned disadvantages.

Another object of this invention is to provide a method for producing a stable, heat-sensitive recording sheet by applying a single coating agent to a support to form a single layer coating heat-sensitive recording sheet.

SUMMARY OF THE INVENTIONv According to the present invention, the heatsensitive recording sheet has a coating comprising a LII uniform dispersion of particles of a component A and a component B as color-forming reaction materials and a component C which is an inhibitor of unusual colordevelopment and is selected from the group consisting of ethylenediamine tetraacetic acid and alkali metal salts thereof. Component A is at least one member selected from the group consisting of the iron salts of aliphatic acids and component B is at least one member selected from the group consisting of 8- hydroxyquinoline and halogen derivatives thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT Component A is at least one member selected from the class of iron salts of aliphatic acids and is reacted with at least one or more compounds selected from the class of 8-hydroxyquinoline and halogen derivatives thereof, i.e. component B, in the presence of an inhibitor of unusual color-development to produce a black color which can then be utilized as a recording image.

Representative examples of component A are the ferrous and ferric salts of aliphatic acids. Preferred aliphatic acids include aliphatic carboxylic acids containing from about 8 to 24 carbon atoms. These include, for example, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, margaric acid, arachidic acid, behenic acid, lignoceric acid, oleic acid, erucic acid, cetolic acid and the like. From a practical point of view, it is preferable to utilize aliphatic acids whose iron salts have a melting point ranging from 50C to 170C.

Representative examples of component B include 8- hyd roxyquinoline of the formula M.P. 76 C.

and halogen derivatives of 8-hydroxyquinoline such as 5, 7-dibromo-8-hydroxyquinoline of the formula and 5-chloro-7-iodo-8-hydroxyquinoline of the formula Other halogen derivatives of S-hydroxyquinoline which may be utilized include 5-bromo-8- hydroxyquinoline, 5-iodo-8-hydroxyquinoline, 5,7- dichloro-8-hydroxyquinoline, 5, 7-diiodo-8- tetraacetic acid and alkali metal salts thereof, can be ammonia 0H);

CHzN(C.H2COOH)2 Disodium or dipotassium ethylenediamine tetraacetate are the preferred alkali metal salts ofEDTA for use in this invention.

Unusual color-forming inhibitors are used in the heat-sensitive copy-sheet of U8. Pat. No. 3,442,682, but the specific combination of components A, B and C of the present invention is not disclosed therein. Chelating agents such as oxalic acid, citric acid, tetaric acid and the alkali metal salts of these acids are normally used as inhibitors of unusual color-development but when these chelating agents are used in the present invention the resulting heat-sensitive recording sheets cannot simultaneously satisfy the three desired product requisites, that is, stability of the coating agent, shelf life of the heat-sensitive recording sheet and the desired characteristics of the recorded images (sharpness, contrast and color-forming sensitivity). On the con trary, the heat-sensitive recording sheets according to the present invention in which ethylenediamine tetraacetic acid or the alkali metal salts thereof are employed as the inhibitor can simultaneously satisfy th above-mentioned three desired requisites.

The proportions of components A, B and C are not critical, but it is preferred to use 100 parts by weight of component A, 500 parts by weight of component B and l 50 parts by weight of component C.

The color tone of the print image obtained by using the heat-sensitive recording sheet of this invention is dark black and the print image is sharp and clear. Therefore, the recording sheet, having print images according to this invention, can be used as an original for reproduction'orprinting by diazograph, electrostatography and electrophotography.

According to another aspect of this invention, white pigments such as zincwhite, white lead, titanium oxide, lithopone, alumina white, calcium carbonate, white carbon, antimony white, basic lead sulfate, lead silicate, zirconium oxide, tin oxide, barium sulfate, barium carbonate, and the like, can be added to the coating agent in order to convert the light brown color of the recording sheet resulting from the iron salt of the aliphatic acid to a whitish color without lowering the overall quality of the print image.

In the preparation of the heat-sensitive recording sheets of this invention, a binder solultion is preferably utilized in addition to the color-forming components A and B, and the unusual color-forming inhibitor, i.e. component C. As the binder component, any wellknown binder can be utilized. These include, for example, gelatin, polyvinyl alcohol, polyvinyl butyral, polyacrylic acid ester, polyacrylamide, polyvinylacetate, polyvinyl chloride, polystyrol, methylcellulose, ethylcellulose, polyamide resin, petroleum resin, terpene resin and silicon resin. As a solvent, any well-known solvent can be utilized such as water,-alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol, ketones such as acetone and methylethyl ketone, esters such as ethyl acetate, aliphatic hydrocarbons such as hexane, heptane and petroleum benzine, halogen compounds such as methylene chloride and benzylchloride and aromatic hydrocarbons such as benzene, toluene and xylene.

It is also preferable to add a solid fatty acid and/or wax to the formulations for the purpose of controlling the color-forming sensitivityand the sharpness. Examples of suitable solid fatty acids include stearic acid and palmitic acid. Examples of suitable waxes include carnauba wax, sperm aceti, paraffin wax, ceresiue wax, microcrystalline wax, fatty acid amide wax, hardened castor oil, and specific synthetic wax.

The heat-sensitive recording sheets of this invention may be prepared by mixing a binder solution, a component A and a component C, grinding and dispersing the mixture by a ball-mill to form one suspension liquid, and mixing a binder solution, a component B and a component C, grinding and dispersing the mixture by a ball-mill to form the other suspension, and then mixing the two suspension liquids with stirring to form a single coating liquid and finally coating the resulting single coating liquid on a base sheet such as paper followed by'drying the resulting coating.

The following examples will serve to illustrate but not to limit the invention. In the following examples, all parts are by weight.

EXAMPLE 1 Formula for suspension liquid A:

Ferric stearate 2 parts Stearic acid 10 parts Vinylbutyral 10 parts Methyl alcohol 20 parts Ethyl acetate 50 parts Formulator suspension liquid B:

8-hydroxyquinoline 2 parts Ethylenediamine tetraacetic acid 2 parts Vinylbutyral l0.parts Methyl alcohol 20 parts Ethyl acetate 50 parts Each of the above-mentioned compositions were prepared in a ball-mill and the resulting suspension liquids A and B were mixed by an agitator to form a homogeneous liquid coating agent. This coating agent was applied to a white paper to form a coating of 5 p. in thickness anddried at a temperature below 40C. The resulting recording sheet gave a clear black image upon heating at a temperature higher than C for 0.05 second.

The coating agent is stable and can be stored for a pe- Y riod of over one week and the heat-sensitive recording sheet itself is also stable and possesses a long shelf life.

The above-mentioned compositions were treated in the same manner as in Example I to form suspension liquids A and B and were applied to a white paper to produce a recording sheet. The resulting recording sheet gave a clear black image upon heating at a temperature over 100C for 0.05 second. Stability of the coating agent and stability of the heat-sensitive recording sheet are as good as those in Example I.

We claim:

1. A heat-sensitive recording sheet containing a coating layer consisting essentially of a uniform dispersion of particles of a. at least one iron salt of an aliphatic acid;

b. at least one halogenated S-hydroxyquinoline; and

c. an inhibitor of unusual color-development selected from the group consisting of ethylene diamine tetraacetic acid and alkali metal salts thereof.

2. The heat-sensitive recording sheet of claim 1 wherein the aliphatic acid is an aliphatic carboxylic acid containing from about 8 to 24 carbon atoms.

3. The heat-sensitive recording sheet of claim 1 wherein the iron salt of the aliphatic acid is ferric stearate.

4. The heat-sensitive recording sheet of claim 1 wherein the iron salt of the aliphatic acid is ferrous palmitate.

5. The heat-sensitive recording sheet of claim 1 wherein the inhibitor of unusual color-development is ethylenediamine tetraacetic acid.

6. The heat-sensitive recording sheet of claim 1 in which X is a halogen and X is a halogen or hydrogen.

10. The heat-sensitive recording sheet of claim 9 wherein X and X are similar or dissimilar and are se lected from the group consisting of chlorine, bromine and iodine. 

1.A HEAT-SENSITIVE RECORDING SHEET CONTAINING A COATING LAYER CONSISTING ESSENTIALLY OF A UNIFORM DISPERSION OF PARTICLESOF A. AT LEAST ONE IRON SALT OF AN ALIPHATIC ACID; B. AT LEAST ONE HALOGENATED 8-HYDROXYQUINOLINE; AND C. AN INHIBITOR OF UNSUAL COLOR-DEVELOPMENT SELECTED FROM THE GROUP CONSISTING OF ETHYLENE DIAMINE TETRAACETIC ACID AND ALKALI METAL SALTS THEREOF.
 2. The heat-sensitive recording sheet of claim 1 wherein the aliphatic acid is an aliphatic carboxylic acid containing from about 8 to 24 carbon atoms.
 3. The heat-sensitive recording sheet of claim 1 wherein the iron salt of the aliphatic acid is ferric stearate.
 4. The heat-sensitive recording sheet of claim 1 wherein the iron salt of the aliphatic acid is ferrous palmitate.
 5. The heat-sensitive recording sheet of claim 1 wherein the inhibitor of unusual color-development is ethylenediamine tetraacetic acid.
 6. The heat-sensitive recording sheet of claim 1 wherein the inhibitor of unusual color-development is disodium ethylenediamine tetraacetate.
 7. The heat-sensitive recording sheet of claim 1 wherein the coating layer contains a white pigment component.
 8. The heat-sensitive recording sheet of claim 1 wherein the coating layer is deposited on a support.
 9. The heat-sensitive recording sheet of claim 1 wherein the halogenated 8-hydroxyquinoline has the formula:
 10. The heat-sensitive recording sheet of claim 9 wherein X1 and X2 are similar or dissimilar and are selected from the group consisting of chlorine, bromine and iodine. 